Reading Preestablished Control Limits

XCHART Statement

Reading Preestablished Control Limits

See SHWXCHR in the SAS/QC Sample Library

In the previous example, the OUTLIMITS= data set GAPLIM saved control limits computed from the measurements in PARTGAPS. This example shows how these limits can be applied to new data provided in the following data set:

   data gaps2;
      input sample @;
      do i=1 to 5;
         input partgap @;
         output;
         end;
      drop i;
      datalines;
   22 287 265 248 263 271
   23 267 253 285 251 271
   24 249 252 277 269 241
   25 243 248 263 282 261
   26 287 266 256 278 242
   27 251 262 243 274 245
   28 256 245 244 243 272
   29 262 247 252 277 266
   30 244 269 263 278 261
   31 245 264 246 242 273
   32 272 257 277 265 241
   33 251 249 240 260 261
   34 289 277 275 273 261
   35 267 286 275 261 272
   36 266 256 247 255 241
   37 291 267 267 252 262
   38 258 245 264 245 281
   39 277 267 241 272 244
   40 252 267 272 245 252
   41 243 241 245 263 248
   ;

The following statements create an $\bar{X}$ chart for the data in GAPS2 using the control limits in GAPLIM:

   title 'Mean Chart for Gap Widths';
   symbol v=dot c=yellow;
   proc shewhart data=gaps2 limits=gaplim;
      xchart partgap*sample / cframe   = vigb
                              cinfill  = vlib
                              cconnect = yellow
                              coutfill = red;
   run;

The chart is shown in Figure 42.7.

The LIMITS= option in the PROC SHEWHART statement specifies the data set containing the control limits. By default,^* this information is read from the first observation in the LIMITS= data set for which

the value of _VAR_ matches the process name PARTGAP
the value of _SUBGRP_ matches the subgroup-variable name SAMPLE

Figure 42.9: $\bar{X}$ Chart for Second Set of Gap Width Data

The chart indicates that the process is in control, since all the means lie within the control limits.

In this example, the LIMITS= data set was created in a previous run of the SHEWHART procedure. You can also create a LIMITS= data set with the DATA step. See "LIMITS= Data Set" for details concerning the variables that you must provide.

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